Generally, a video stream must first be decoded and converted to be capable of being displayed on an entertainment device, such as a television. For example, an MPEG transport or program stream usually moves through a system including several components before being in the correct format to be viewed on a display.
The type of system used in decoding and converting the video streams for display may include a demultiplexer and a decoder. The demultiplexer extracts the information in the transport layer or program layer. The demultiplexer then outputs elementary streams to a video decoder, an audio decoder, or both.
The video decoder receives the video elementary stream, decodes it, and outputs the decoded video signal. For an MPEG stream, the decoded video signal is usually in a form of CCIR656 standard. The decoded video signal is then received by a digital-to-analog converter to be converted to an analog RGB signal which may be displayed on a display type device. Other components that may come into play include formatters such as a 656 formatter, and additional memory.
For many display devices, portions of the picture are trimmed for display after the decoding process so that the pictures may fit correctly onto the display device screen. One example may include cutting a portion of the left end of the picture and cutting a portion of the right end of the picture for the end display. However, generally decoding of an entire picture is done before this type of trimming and scaling to display occurs. Since the entire picture is decoded, the decoded data is saved to one or more components. What is needed is a video decoder to trim the picture during the decoding process itself thereby saving both memory space and processor efficiency.